Run A Lawnmower on Diesel With Hot Bulb Hack

If you’re into automotive hacks and don’t watch [Robot Cantina], you are missing out. This hack has [Jimbo] taking a break from automotive hacking to butcher a poor, innocent Tecumseh …read more

Jun 10, 2025 - 01:10

Run A Lawnmower on Diesel With Hot Bulb Hack

If you’re into automotive hacks and don’t watch [Robot Cantina], you are missing out. This hack has [Jimbo] taking a break from automotive hacking to butcher a poor, innocent Tecumseh lawnmower to run diesel fuel (or anything else) by converting the motor into a hot bulb engine. (Video embedded below.)

The secret is a long stack of anti-fouling adapters, which are essentially extension tubes that move the spark plug out of the combustion chamber to keep it from getting crudded up in an engine that’s burning too much oil. In this case, burning is what’s happening inside the anti-fouling adapters: by stacking seven of them, [Robot Cantina] is able to create a hot-bulb– volume that stays hot enough between strokes to induce spontaneous combustion of the fuel-air mix.

Hot-bulb engines were popular for certain tractors (the Lanz Bulldog being the most famous) and stationary engines from the late 19th century until Rudolf Diesel’s eponymous invention drove them out of their niche completely sometime after WWII.

Traditionally, a torch would have been used to heat the hot bulb, but here [Jimbo] starts the engine on gasoline with a spark plug at the end of the stack, and disconnect the spark once the hot bulb has warmed sufficiently. Given how rough the engine runs before the ersatz hot bulb heats up enough for spontaneous combustion, tradition seems like the way to go. Even once heated up, the “chaos in the combustion chamber” (probably knocking) is enough to pop the (now disconnected) spark plug from the end of the stack of adapters at one point.

While shockingly an inspection revealed no obvious damage to the engine after the first day’s experiments, this is probably not a hack you would want to use on a motor you intended to keep — or run for very long, for that matter. Practical or not, it is fascinating to know you can go back in time to the hot-bulb era with such a simple modification. Watching this motor pop and snarl while drinking down diesel fuel, acetone, or 190 proof alcohol is a bit like watching the proverbial dancing bear: the point is not how well it dances, but that it can dance at all. If you can’t get enough of it, they made a second video that features further fuel-testing fun, and even a mowing montage.

We’ve featured other [Robot Cantina] hacks that were arguably more practical, like hacking an old Saturn’s ECU to allow for Honda Insight-style lean burning or this DIY dynomometer for similarly small engines.